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Filters can be used for a number of different reasons such as reducing the light entering the lens allowing the shutter to stay open longer for slow shutter speed effects, adjusting the strength of reflections on the surface of water or simply adding more colour to an image.

ND (Neutral Density) Filter

ND filters reduce the amount of light and colours that enter the lens in equal amounts giving you a greater choice of aperture and shutter speed.  This is particularly useful when trying to achieve slow shutter speed effects during the day or in lighter conditions as the shutter speed can be slowed without over exposing the image.  ND filters can be obtained in a number of different ’strengths’ for use in different conditions.

ND filters can also be graduated and used for conditions where part of the scene is brighter than others.

An example of how an ND filter can be used is below, the image was taken during the day at a shutter speed of 8 seconds, this would have completely over exposed the photo if the ND filter(s) had not been used.  Using the ‘Cokin’ filter attachment you can also use 1, 2 or even 3 ND filter at once to give greater flexibility of your aperture and shutter speed settings.

Slow shutter speed weir

IR (Infrared) Filter

An IR filter will block visible light and only allow infrared light to pass through to the camera lens.  The part of the spectrum that infrared uses is referred to as near infrared, this is different from far infrared, which is used in thermal imaging.  Infrared filters will turn the sky very dark, greens can appear almost white.  Some excellent examples of Infrared photography can be found in this gallery of photos by Allon Kira.

By: Werner Kunz (werkunz1)

Polarizing Filter

A polarizing filter can be used to darken skies increasing the contrast between the clouds and the sky.  Heat haze and reflected sunlight are reduced, and in color photographs saturation is increased. Polarizers can be used when taking images involving reflectadions, such as those of water or glass as the reflections can be reduced.

Credit: INoxKrow

The Polarizer filter  effect can clearly be seen in the example image above.

UV (Ultra Violet) Filter

UV filters are used to reduce haziness created by ultraviolet light. A UV filter is mostly transparent to visible light, and can be left on the lens for nearly all shots. A strong UV filter cuts off some visible light in the violet part of the spectrum, and so has a pale yellow color.  Strong UV filters are also sometimes used for warming color photos taken in shade with daylight-type film.

Colour Filters

Filters can be purchased in a variety of colours, these can be solid colours or graduated.  Colours such as orange or red can be used to exaggerate the colour in a sunset photo for example whereas blues could be used when taking photos of the sea.  In the image below a blue graduated filter has been used to effect the bottom half of the image and a purple filter for the top half.

Colour filter example

Star Filters

Star filters (or cross screen filters) create points of light,  streaking outward from a central source of light.  This can make lighting within the scene take on a more dramatic appearance.  This effect is produced by a series of thin lines etched onto the surface of a clear filter.

Credit: ddamredhead